418 MISS B. MURIEL BRISTOL ON A 
genera, Characium* and Chlorochytrium t, but it points to the fact that either 
the conditions were abnormal or else the genus Chlorococcum is somewhat 
primitive. 
The aplanospores thus produced remain enclosed for a considerable time 
within the old mother-eell-wall, which gradually disintegrates to form a 
mucilaginous stratum in which the young cells are imbedded, and the alga 
enters into a palmella-like condition. In this state further division of the 
young cells into two or four daughter-cells may take place by successive 
bipartition, and strata of considerable extent may be formed; but no 
cellulose walls appear, and the cells remain imbedded in a mass of mucilage. 
A sudden change in external conditions, with its accompanying physiological 
shock, induces the formation of cilia either at once or after one or two 
further divisions, and the cells, becoming motile, swim away rapidly from 
the mucilaginous stratum. Fusion of these zoogonidia has frequently, 
though not always, been observed, and develpment takes place in exactly 
the same way as in the normally produced zoogonidia. 
The observation of this delayed production of ejia by the palmelloid cells 
is interesting in that it indicates that the aplanospores are really reduced 
zoogonilia, but that the surrounding nutrient conditions are such as to be 
able to support the development of a large number of individuals in a small 
spaee, and to render their wider distribution unnecessary. 
The zoogonidia produced in this manner are oval and are larger than those 
formed normally. They vary considerably in size, being from 5 to 9°5 w in 
breadth and from 9'7 to 14:5 w in length according to the number of 
preliminary ‘divisions of the cell. Each contains a single bell-shaped 
chloroplast lining the posterior end of the cell, and in some cases the 
chloroplast is somewhat irregular in thickness forming cushion-shaped 
projections into the interior of the cell. There is a bright red pigment-spot 
at the anterior end, and a single pyrenoid in the chloroplast. In certain 
circumstances the pa'melloid cells gradually become spherical and develop 
into vegetative cells. 
It is characteristic of this genus that true vegetative division does not take 
place. In some cases the contents of a cell divide into two parts, but the 
two daughter-cells invariably secrete new cell-walls, and the mother-cell-wall 
becomes converted into mucilage. The two danghter-cells remain loosely 
attached to one another, and, as a result of further similar divisions, small 
clusters of cells are formed (figs. 4-8). Multiplication of this kind, which 
appears to be a modified formation of aplanospores, appears to take place 
* Smith, G. M., *Zoospore Formation in Characium Steboldii, A. Dr.," Ann. Bot. 
vol. xxx. no. cxix. July 1916. 
t Bristol, B. M., “On the Life-history and Cytology of Chlorochytrium grande, sp. nov." 
Ann. Bot, vol, xxxi. no. cxxi. Jan, 1917. 
